One difference that seems relevant is that math is a general discipline/skillset that has applicability to a variety of career paths and industry sectors, and a

One difference that seems relevant is that math is a general discipline/skillset that has applicability to a variety of career paths and industry sectors, and also can be a base/prerequisite requirement when pursuing further education in fields that don't necessarily seem very "mathy". In other words, one often doesn't necessarily study math to become a professional mathematician, but as a means to another end, such as providing a grounding to enable meaningful study in another area (a psychology degree requiring study of statistics would be one example). Nursing, on the other hand, is in itself a vocation. One studies nursing, presumably, to become a nurse, and not usually as a means to some other end. Therefore, a lack of boys' interest in math would be potentially different from a lack of boys' interest in nursing, in that innumeracy (just like illiteracy) tends to limit individual outcomes much more severely than lack of interest in a particular vocational path such as nursing.